River ecosystem processes: A synthesis of approaches, criteria of use and sensitivity to environmental stressors (original) (raw)
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Redefinition and Elaboration of River Ecosystem Health: Perspective for River Management
Hydrobiologia, 2006
This paper critically reviews developments in the conceptualization and elaboration of the River Ecosystem Health (REH) concept. Analysis of literature shows there is still no consistent meaning of the central concept Ecosystem Health, resulting in models (i.e. elaborations) that have unclear and insufficient conceptual grounds. Furthermore, a diverse terminology is associated with describing REH, resulting in confusion with other concepts. However, if the concept is to have merit and longevity in the field of river research and management, unambiguous definition of the conceptual meaning and operational domain are required. Therefore a redefinition is proposed, based on identified characteristics of health and derived from considering semantic and conceptual definitions. Based on this definition, REH has merit in a broader context of river system health that considers societal functioning next to ecological functioning. Assessment of health needs integration of measures of multiple, complementary attributes and analysis in a synthesized way. An assessment framework is proposed that assesses REH top-down as well as bottom up by combining indicators of system stress responses (i.e. condition) with indicators identifying the causative stress (i.e. stressor). The scope of REH is covered by using indicators of system activity, metabolism (vigour), resilience, structure and interactions between system components (organization). The variety of stress effects that the system may endure are covered by using biotic, chemical as well as physical stressors. Besides having a unique meaning, the REH metaphor has added value to river management by being able to mobilize scientists, practitioners and publics and seeing relationships at the level of values. It places humans at the centre of the river ecosystem, while seeking to ensure the durability of the ecosystem of which they are an integral part. Optimization of the indicator set, development of aggregation and classification methodologies, and implementation of the concept within differing international frames are considered main aims for future research.
Perspectives on the functional assessment of multi-stressed stream ecosystems
Freshwater Science
Past research has examined how anthropogenic stressors affect both structural and functional attributes of stream ecosystems. Nevertheless, biomonitoring programs rely mostly on structural metrics for surface-water quality and status assessments, and few studies have examined the extent to which functional metrics can strengthen these structure-based assessments. We reviewed studies that combined the response of stream-ecosystem structural and functional measures to single and multiple stressors. These studies illustrate that structural and functional measures can respond in similar, complementary, or even contradictory magnitude and direction to different stressors. Because of this complexity, we suggest that a combination of structural and functional measures may provide added information on surface-water quality and status, especially when ecosystems are affected by multiple stressors. Better knowledge about trophic and non-trophic roles of dominant taxa and the effects of changes in species diversity on stream ecosystem processes could improve understanding of the relationships among structural and functional measures. Based on our review, we suggest that future research should be designed to: 1) increase understanding of the roles of individual species and communities in the functioning of stream ecosystems, and 2) quantify the responses of individual species and communities to individual stressors and combinations of multiple stressors. We propose that increasing the knowledge base about the suites of traits that occur in different species, how these traits coevolved under local environmental abiotic and biotic conditions, and how they interact is needed to understand how multiple stressors affect ecosystem structure and function. This trait-based knowledge is essential to understanding the relationship between structure and function in multi-stressed stream ecosystems and could help managers to make stronger inferences about the combined effects of multiple stressors on water quality and status.
Journal of the North American Benthological Society, 2008
River health monitoring traditionally has made use of structural measurements (water quality or taxonomic composition of aquatic organisms). We argue that a more complete assessment of river health should include functional metrics, such as rates of organic matter decomposition and ecosystem metabolism. Leaf breakdown links the characteristics of riparian vegetation with the activity of both aquatic invertebrates and microbial organisms and is affected by natural and human-induced variation in a wide range of environmental factors. Measurement of leaf breakdown is relatively simple and has modest equipment requirements. River metabolism (gross primary productivity and ecosystem respiration) measures the rates of production and use of organic C in river ecosystems as a whole, providing a direct estimate of the food base that determines life-supporting capacity. Metabolism measurements require more sophisticated equipment than do measurements of leaf breakdown, but improvements in technology have made metabolism measurements relatively easy. We review the factors that influence leaf breakdown and river metabolism and pay particular attention to the effects of human-induced environmental stressors. We also describe how measurements can be standardized and suggest criteria for interpreting functional measures in terms of river ecosystem health. Last, we consider the strengths and weaknesses of both methods as functional measures and provide recommendations for their use as biomonitoring tools.
Frontiers in Ecology and Evolution, 2023
Opportunities to understand and protect natural aquatic diversity in both relatively pristine and managed rivers can be enhanced with a comprehensive, system-wide understanding of a river's hydrogeomorpholgy and its effects on ecological structure and functioning from the river's headwaters to its terminus in an ocean, lake, or natural endorheic basin. While a moderate number of macrosystem ecology studies have been undertaken recently in headwaters, comparable ecological approaches to studying whole rivers or at least their larger components from upstream to downstream are relatively rare. This is partially correlated with the paucity of applicable river ecosystem models developed over the last half century which could otherwise provide diverse, testable tenets (hypotheses). This manuscript focuses on a 15+ year updated, system-wide analysis of the applicability of the 17 tenets included in our previously published, lotic model-the Riverine Ecosystem Synthesis, or RES. We also propose here four new tenets and analyze the system-wide applicability of the revised RES. Those new tenets hypothesize that: (H-18) "The range and degree of impacts of a Functional Process Zone on biodiversity and ecological processes differ among several factors, including types of FPZs, total river area covered, and dependent variables examined, even in the same river network position"; (H-19) "The degree of ecological differences among types of FPZs vary seasonally with the process being examined while also differing among types of life history characteristics-especially when contrasting responses among seasonal periods of either maximum or minimum growth and reproduction"; (H-20) "The relative importance of in-stream versus watershed drivers of ecological processes in streams can vary within macrosystems and among ecoregions and partially depends on elevation, terrestrial characteristics (natural or human modified), and FPZ type and extent"; and (H-21) "The provision of ecosystem services varies significantly with FPZ type, river size, and location vis-Ã -vis human populations". Where appropriate, we also evaluate aspects of several other models published by colleagues that pertain to river ecology.
Ecosystem measures of river health and their response to riparian and catchment degradation
Freshwater Biology, 1999
1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems. 2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R 24 ) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality. 3. Baseline measurements of GPP and R 24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R 24 ) was used to determine whether sites were net consumers (P < R) or producers (P > R) of carbon but this was not considered a reliable indicator of stream health on its own. 4. Although forest streams were typically net consumers of carbon (P < < R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes. 5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R 24 , especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.
Integrated Environmental Assessment and Management, 2009
This is 1 of 12 papers prepared by participants attending the workshop ''Risk Assessment in European River Basins-State of the Art and Future Challenges'' held in Liepzig, Germany on 12-14 November 2007. The meeting was organized within the framework of the European Commission's Coordination Action RISKBASE program. The objective of RISKBASE is to review and synthesize the outcome of European Commission FP4-FP6 projects, and other major initiatives, related to integrated risk assessment-based management of the water/ sediment/soil environment at the river basin scale.
Understanding hydro-ecological surprises for riverine ecosystem management
Current Opinion in Environmental Sustainability, 2018
Human interference within riverine systems has substantially altered the regimes of the natural hydrological cycle. This can be characterised by large changes in water discharge and sediment fluxes which have led to degradation of riverine ecosystems and biodiversity across many large river basins of the world, resulting in hydro-ecological surprises. This review summarizes major unknowns including human environment interactions and hydrological alterations and how they lead to degradation of riverine ecosystems through different biogeochemical processes. It proposes to identify the state of riverine ecosystems using a stress-strain analysis approach and to develop integrated interdisciplinary modelling for supporting conservation, adaptation or transformation strategies for riverine ecosystem management at different states.
Frontiers in Ecology and the Environment, 2014
R iverine ecosystems are some of the most diverse on Earth and provide important services (Palmer and Richardson 2009; Strayer and Dudgeon 2010). Understanding how they function is critical to sustainable management but challenging given their complex spatial and temporal structure and multi-scale processes. Riverine systems comprise hydrological-ecological networks organized by the flow of water, sediment, nutrients, and organisms downhill and downstream and the active movement of animals uphill and upstream. Rivers are multidimensional, including longitudinal (upstream-downstream), lateral (upland to channel), vertical (hyporheic, or the zone below the stream bed), and temporal components (Ward 1989; Fausch et al. 2002). Despite this multidimensionality, many ecological processes are influenced by the rapid flow of water downhill, providing strong directional connectivity (Wiens 2002). Rivers are also organized hierarchically, with fine-scale structures (eg gravel patches) embedded within channel bed features (eg riffles), which in turn are embedded within reaches, valley segments, basins, and regions (Table 1; Frissell et al. 1986; Thorp et al. 2008). Uplands are fundamental to riverine organization, with variations in land use, land cover, and soils influencing surface-water and groundwater flow paths, thereby altering water, nutrient, and sediment fluxes to rivers (eg Lewis and Grimm 2007). Rivers are also temporally variable, partially due to hydrology that varies within and across basins and climatic regions (Poff et al. 1997). Thus, we define riverine macrosystems as hierarchical dynamic networks, influenced by strong directional connectivity that integrates processes across multiple scales and broad distances through time (Figure 1; see Heffernan et al. [2014] for macrosystem definition). Ecologists have typically studied riverine ecosystems at the scale of bed features or reaches distributed longitudinally along rivers of varying size, in an attempt to understand the strong influences that upstream and watershed processes, including human modifications, can have (Poole 2010). Our conceptualization of rivers and watersheds as "macrosystems" is a logical extension of these approaches (Figure 1). We view riverine macrosystems as repeating, interacting MACROSYSTEMS ECOLOGY
Linking the physical form and processes of rivers with ecological response
IAHS-AISH publication, 2002
Fluvial eco-geomorphology seeks to link the physical form and processes of rivers with ecological responses by adopting an ecosystem perspective in research and management. It is recognized that the physical habitat is not static, and there are numerous and complex interconnections at various scales that determine fluvial form and processes. In turn, the physical environment exerts a strong control on river biota, but the effects can be indirect and mediated through complex interactions. As a consequence, there are considerable uncertainties in manipulating fluvial systems; hence an adaptive approach to management is required. Contributions from papers presented from the session on eco-geomorphology in the IAHS-ICCE-UNESCO International Symposium on the Structure, Function and Management Implications of Fluvial Sedimentary Systems are discussed in the context of two major themes of ecosystem management: physical habitat improvement and restoration of flow regimes. Challenges and opp...
Multiple stressors in coupled river-floodplain ecosystems
Freshwater Biology, 2010
1. Riverine floodplains are highly complex, dynamic and diverse ecosystems. At the same time they are among the world's most threatened ecosystems because of the pervasiveness of dams, levees and other factors such as rapid spreading of non-native species. Hence, floodplains are ideal systems to study ecological impacts of multiple stressors at the local, regional and catchment scale. 2. Concepts such as the subsidy-stress hypothesis and the stress-induced community tolerance concept have been formulated to study the effect of stressors on aquatic and terrestrial ecosystems, as well as on their functional linkages. 3. Riverine floodplains are pulsed ecosystems with distinct flow, sediment, resource and thermal pulses -thereby creating distinct 'windows of ecological opportunity'. Human modifications that truncate or amplify theses pulses will have cascading effects on riverfloodplain interactions by shifting the thresholds of connectivity, resilience or resistancecausing drastic regime shifts. 4. Most aquatic insects and pond-breeding amphibians have complex life cycles with aquatic and terrestrial stages. They are exposed to different stressors in their aquatic and terrestrial realm. Because most life history functions of aquatic insects are restricted to a short terrestrial period, we need to fully integrate the 'airscape' into the future management of river-floodplain ecosystems. 5. Riverine floodplains integrate and accumulate multiple stressors at the catchment level, as reflected by distinct catchment fingerprints. Based on the European Catchment Data Base we provide spatially explicit information on multiple stressors; a key prerequisite for setting priorities in conservation and management planning. 6. Thematic implications: the management of stressed river and floodplain ecosystems is a major challenge for the near future and water managers worldwide. Management approaches need to be adaptive and embedded within a catchment-wide concept to cope with upcoming pressures originating from global change.